salvage patients with persistent hypoxemia when on conventional mechanical ventilation or, in some cases, used as a primary modality of ventilatory support from the start. High-frequency flow interruption HFFI — High Frequency Flow Interruption is similar to high-frequency jet ventilation but the gas control mechanism is different. Frequently a rotating bar or ball with a small opening is placed in the path of a high pressure gas. As the bar or ball rotates and the opening lines-up with the gas flow, a small, brief pulse of gas is allowed to enter the airway. Frequencies for HFFI are typically limited to maximum of about 15 hertz. High-frequency ventilation (active) High-frequency ventilation (active) — HFV-A is notable for the active exhalation mechanic included. Active exhalation means a negative pressure is applied to force volume out of the lungs. The CareFusion 3100A and 3100B are similar in all aspects except the target patient size. The 3100A is designed for use on patients up to 35 kilograms and the 3100B is designed for use on patients larger than 35 kilograms. CareFusion 3100A and 3100B High-frequency oscillatory ventilation was first described in 1972 and is used in neonates and adult patient populations to reduce lung injury, or to prevent further lung injury. HFOV is characterized by high respiratory rates between 3.5 and 15 hertz (210 - 900 breaths per minute) and having both inhalation and exhalation maintained by active pressures. The rates used vary widely depending upon patient size, age, and disease process. In HFOV the pressure oscillates around the constant distending pressure (equivalent to mean airway pressure [MAP]) which in effect is the same as positive end-expiratory pressure (PEEP). Thus gas is pushed into the lung during inspiration, and then pulled out during expiration. HFOV generates very low tidal volumes that are generally less than the dead space of the lung. Tidal volume is dependent on endotracheal tube size, power and frequency. Different mechanisms (direct bulk flow - convective, Taylorian dispersion, Pendelluft effect, asymmetrical velocity profiles, cardiogenic mixing and molecular diffusion) of gas transfer are believed to come into play in HFOV compared to normal mechanical ventilation. It is often used in patients who have refractory hypoxemia that cannot be corrected by normal mechanical ventilation such as is the case in the following disease processes: severe ARDS, ALI and other oxygenation diffusion issues. In some neonatal patients HFOV may be used as the first-line